Can top construction and method of fabrication

ABSTRACT

A tear strip for a can top is formed by first forming a narrow groove having a central portion which defines the tear strip edge and inclined walls on the opposite sides of such central portion, and thereafter scoring the central portion of the groove to form the tear strip. The stress attendant to scoring is absorbed by the inclined opposite walls rather than being transmitted to the remainder of the can top metal.

United States Patent 1 1 3,563,199

[72] Inventor Wayne F. Wolfe [56] References Cited 0 1 111 6 Calif.UNITED STATES PATENTS 1 PP 7 5 2041,912 5/1936 Fabrice 113/15 1 PM15,1963 3,254,790 6/1966 Dunn 220/54 [45] Patented Feb. 16, 1971 1 l. 24 [73] Assignee Hunt Foods and Industries, Inc. 3325043 6/1967 Hencherta 20/5 Fullerton, Calif. FOREIGN i T N Original application June 22,1966, Ser. 557,256 1 1/ l 943 Great Brltam. 59511 now abandoned PrimaryExaminer- Lowell A. Larson Attorney-Fowler, Knobbe & Martens [54] CANTOP CONSTRUCTION AND METHOD OF FABRICATION ABSTRACT: A tear strip for acan top is formed by first form- 4 Clams l0 Drawmg Figs ing a narrowgroove having a central portion which defines the [52] U.S. Cl. 113/121,tear strip edge and inclined walls on the opposite sides of such 220/54central portion, and thereafter scoring the central portion of [SI] Int.Cl. B2ld 51/38 the groove to form the tear strip. The stress attendantto scor- [50] Field of Search 1 ing is absorbed by the inclined oppositewalls rather than 13/ 15, 1200, 121C; 220/27, 53, 54 being transmittedto the remainder of the can top metal.

tented Feb. 16, 1971 2 Sheets-Sheet 1 26 EGG.

YNVENTOR W y/VE A 14/0055 Patented Feb. 16,1971 3,563,199

2 Sheets-Sheet 2 INVENTOR. W/WNE 1? W04 FE CAN TOP CONSTRUCTION ANDMETHOD OF FABRICATION This is a division of application Ser. No. 559,511, filed Jun. 22, I966, now abandoned.

CAN TOP CONSTRUCTION AND METHOD OF FABRICATION This invention relates tocans which have removable strips of various shapes on their ends so thatthe cans may be opened by manually tearing the strip from the can endand to a method of fabricating such can ends.

Cans which have a tear strip on one end generally are of two types--those in which the tear strip defines a limited opening for pouring outthe contents and those in which the tear strip is formed around theperiphery of the can end so that the central panel of the end is removedwith the tear strip. The former type are often referred to as pop top"cans and are widely used for beverages, whereas the latter type aresometimes referred to as zip top" cans and are more popular for holdingsolid or semiliquid materials.

Both types generally have been fabricated by stamping the can end toscore the outline of the tear strip. The strip can then be removed bypulling a tab attached to the strip to tear it loose from the can end.

Before the advent of the scored can ends, most can tops were made ofsteel. However, scoring these lids has created a number of problems.Unfortunately, the scoring dies work harden the can ends adjacent thescore. Moreover, in scoring lids by prior art methods, the scoring diehas a tendency to buckle the can end because of the tremendous stressesset up in the relatively thin panel as the metal is literally pushedaway,

from the score. The buckled lid often flexes up and down as the can ishandled in packaging, shipping and displaying. Moreover, the can isparticularly subjected to rough handling by the consumer who throws itinto a shopping basket. As the lid flexes, the brittle, work-hardenedsteel frequently cracks at the minimum thickness defined by the scorecausing the can to leak. Needless to say, even a pinhole air leak cancause the contents of the can to spoil. This not only results in adissatisfied customer, by may create substantial legal liabilities aswell. I

In an effort to avoid these shortcomings, many can rnanufactures havestarted using aluminum. It is more ductile than steel and does notbecome work hardened or as brittle when stamped by the scoring die. Infact steel has largely been replaced by aluminum in the fabrication ofcan ends having tear strips even though the tin-plated steel ends aregenerally more economical than aluminum ends and are also preferred foruse with certain food products.

The present invention overcomes the disadvantages of prior arttechniques to provide a steel can end having a tear strip which does nottend to leak due to excessive buckling when it is formed. The improvedcan end disclosed herein is obtained by a novel method of forming thescore. In accordance with this method, an elongate groove or channel isformed along the portion to be scored, and the canend is grippedadjacent the groove as the central portion of the groove is stamped toscore the outline of the tear strip. The stress from the stampingdeforms the walls of the narrow, preformed groove rather than bucklingthe entire can end diaphragm. Although the metal adjacent the score markis work hardened, the lid is not buckled and therefore does not tend toflex with the consequent loss of the airtight integrity of the can.

A container end fabricated in accordance with this invention is arelatively thin metal sheet forming a taut diaphragm with an elongatescore in the sheet. An elongate buffer formed in the sheet cooperateswith the score to absorb any buckling stresses transmitted away from thescore. Generally, the score defines an edge of a tear strip and a tab isfixed to one end of the strip for use in manually tearing the strip fromthe can end. In an exemplary embodiment, the buffer is a groove havingsidewalls transverse to the diaphragm disposed on opposite sides of thescore. The groove is substantially deeper than the thickness of thesheet from which the can end is formed to make certain the stressaccumulates in the inclined walls of the groove and not in the diaphragmproper.

Inasmuch as the can end fabricated in accordance with this inventiondoes not involve any complex fabrication steps, it can be formed usingconventional can forming machinery. Thus, it is economically competitivewith prior art forms of can ends, yet it overcomes the tendency of theprior art scored steel ends to break down at the score.

These and other features, objects and advantages of this invention willbe apparent from thefbllowing detailed description when read withreference to the accompanying drawings in which:

FIG. 1 is a perspective view of an exemplary can including alidconstructed in accordance with this invention;

FIG. 2 is an enlarged partial vertical section through the tear stripportion of the lid taken generally along lines 2-2 of FIG. 1 showing theprofile of the tear strip portion of the lid, and particularly showingtwo portions of the groove in which the score is located;

FIGS. 3-6 are enlarged vertical sections through a steel sheet andexemplary stamping dies showing the sequential steps for forming agroove and scoring a lid in accordance with the method of thisinvention;

FIG. 7 is a partial vertical section through a representative prior artscored steel can end showing the buckling of the end and the tendency ofthe buckled end to flex; and,

FIGS. 8-l0 are enlarged partial vertical sections through can lidsconstructed in accordance with this invention showing several modifiedgroove shapes and score locations.

Referring first to FIG. I, anexemplary can 2 is illustrated with the lidor upper end 4 having a removable tear strip 6 or pop top fabricated inaccordance: with the teaching of this invention. The particularconfiguration of the tear strip is exemplary only, as this invention isapplicable to other types and shapes of strips.

The can includes a conventional cylindrical can body 8 and aconventional bottom 10. The lid 4 is fabricated of a relatively thinsheet which may, for example, be tin-plated steel. A score 12 outlinesthe tear strip 6 on the lid and a finger tab 16 is affixed at one end ofthe strip 6 by a weld I8. The tear strip 6 is removed by pullingupwardly and outwardly on the tab 16 to tear the strip loose from thecan top along the score I2.

Referring now to FIG. 2, the can end 4 is taut and its major portion isparallel to the plane p. The score 12 is disposed in the valley of adepressed groove 20 which follows a particular configuration to definethe edges of the tear strip 6. The generally U-shaped groove 20 has apair of outwardly sloped sidewalls 22 depending from the diaphragm ormain panel 24 and a central wall portion 26. The sidewalls 22 areinclined at an acute angle 9 relative to the plane p, greater than 60having been found satisfactory.

The score 12 is disposed along the middle of the central wall 26 of thegroove. The width a of the groove 20 is narrow rela tive to the overalldiameter of the can lid t so that the groove itself is not likely to beflexed during handling, e.g. by a persons thumb. In no event should thegroove 20 be wider than one-eighth inch and preferably it isconsiderably narrower than that. The depth b of the groove is at leastseveral times the thickness 0 of the steel plate, which by way ofexample is often between 0.006 and 0.0l 1 inches for a tin-plated steellid. With can ends of this thickness it has been found satisfactory topenetrate about 40 percent to GOpercent of the thickness c of the lidwith the score 12.

Referring to FIGS. 3-46, an exemplary method of fabricating the groove20 and scoring the tear strip 6 is illustrated. Initially, the thinsteel sheet 28 is gripped between two pairs of pressure pads 30 and 32which are spaced apart by approximately the desired width 0 of thegroove 20 (see FIG. 3). A die member 34, having a tapered generallyU-shaped forming it is preferred that the pressure pads 30 and 32 permitsome metal from the diaphragm portion 4 of the steel sheet 23 outsidethe confines of the pads 30 and 32 to creep into the groove area so thatthe walls 22 and 26 of the groove are not stretched too thin by thedeformation.

After the groove 20 has been formed, two pairs of gripping pads 33 and40 are clamped on opposite faces of the diaphragm 28 adjacent the groove(See FIG. The lower gripping pads 40 are joined by a central die member42 which acts as a stop for the convex side of the groove central wall26. With the can end tightly clamped, a scoring die 44 is brought downto stamp a score 12 into the central wall 26 of the groove 20. As thescoring die 44 penetrates the steel sheet, stresses move transverselyfrom the score line 12 as excess metal is literally pushed away from thescore. However, the stress and creep is absorbed or buffered in theinclined walls 22 of the groove which tend to buckle rather thantransmit the stress into the plane of the diaphragm. Thus, although thesteel adjacent the score 12 is work hardened, the diaphragm 4 itself isnot buckled, all the buckling being confined to the walls 22 of therelatively narrow groove.

While FIGS. 36 illustrate only the forming of the score at one portionof the tear strip edge, it is to be understood that the shape of thegroove and the scoring die 44 conform to any desired outline of the tearstrip 6.

Referring to FIG. 7 a representative prior art scored lid 46 isillustrated. As the prior art lid has no groove portion surrounding thescore 48 to absorb the scoring stress, the major portion of the lid 46has buckled under' the stress of the scoring die. Thus, for example, thelid 46 is normally bowed upward, until it is pressed downward to thephantom position 46' as it is handled. It may then pop back upward andmay be reverse flexed numerous times before ultimately being opened forconsumption of the contents. As noted above, the steel adjacent thescore 38 is relatively brittle because it has been work hardened by thescoring die. Thus, the numerous flexures tend to overstress the scoredsteel and cause it to crack at the brittle score 48. On the other hand,the can ends in accordance with this invention have virtually eliminatedthis problem by confining the buckling to the groove walls.

In addition to avoiding leaks at the brittle score, the can endconstruction and fabrication method taught by this invention areadvantageous with respect to other container ends such as those coatedwith a nonelastic material which might crack if the container end isflexed.

Referring now to FIG. 8, a modified profile of the tear strip isillustrated in which the strip 6 is raised relative to the main panel 4'of the can end and a pair of oppositely oriented grooves 2t) and 56forming somewhat of an S-shaped cross sectional configuration aredisposed on each side of the tear strip 6. The score 12 is disposed inthe central wall 26 ofone groove 20 of each pair, and the stresses fromthe scoring operation are taken up in the walls 22' and 52 of thegrooves in a manner similar to that described above with reference tothe embodiment of FIG. 2.

FIG. 9 illustrates another modified profile in which the tear strip 6 isin the same plane as the main panel 4" but the grooved portion 20" israised rather than depressed relative to the can end so as to be convexrather than concave to the can exterior side 53. Moreover, the groove20" includes a rib 54 at the juncture of each inclined wall 20" with thecentral wall 26" on opposite sides of the score 12". The ribs 54strengthen the edge of the tear strip 6" as the strip is removed and theedge of the can end remaining thereafter.

FIG. 10 illustrates yet another modified embodiment of the can endconstructed in accordance with this invention, The embodiment of FIG. 10is quite similar to that illustrated in FIG. 2 except that the score 12"is on the underside or interior side 56 of the can top.

While this invention has been described with reference to a particularshape of tear strip and particular fabricating equipment, the disclosedembodiments are intended to be exemplary only and the invention shouldnot be limited except in accordance with the following claims.

I claim:

tear strip and a pair of inclined walls on opposite sides of the centralportion; and I after said groove has been formed, scoring the centralpor tion of the groove so that the stress resulting from the stamping isabsorbed in the inclined walls rather than being transmitted to theremainder of the sheet.

2. The method of forming a scored tear strip on a can end, comprisingthe steps of:

forming an elongate narrow groove in a metal sheet, said groove having acentral portion defining an edge of the tear strip and a pair ofinclined walls on opposite sides of the central portion;

gripping the sheet adjacent the groove; and

scoring the central portion of the groove of the gripped sheet after thegroove has been formed so that the stress resulting from the stamping isabsorbed in the inclined walls rather than being transmitted to theremainder of the sheet or to the tear strip.

3. A method of forming a can end having a manually removable tear stripthereon, including the following steps in the order recited:

clamping a relatively thin steel sheet on opposite sides of at least oneelongate portion;

forming an elongate buffering groove in said elongate portion of theclamped sheet having opposite sidewalls inclined at between about 60 andwith respect to the major portion of the lid, and a central wall joiningthe sidewalls;

clamping the sheet on opposite sides of the groove; and

stamping a score in the central wall of said groove of the clamped sheetto define the edges of a manually removable tear strip.

4. The method of forming a scored tear strip on a steel can end inaccordance with claim 1 wherein the step of forming the groove includesthe step of forming the groove to a depth at least several times thethickness of the sheet.

1. The method of forming a scored tear strip on a steel can end,comprising the steps of: forming an elongate narrow groove in a steelsheet, said groove having a central portion defining an edge of the tearstrip and a pair of inclined walls on opposite sides of the centralportion; and after said groove has been formed, scoring the centralportion of the groove so that the stress resulting from the stamping isabsorbed in the inclined walls rather than being transmitted to theremainder of the sheet.
 2. The method of forming a scored tear strip ona can end, comprising the steps of: forming an elongate narrow groove ina metal sheet, said groove having a central portion defining an edge ofthe tear strip and a pair of inclined walls on opposite sides of thecentral portion; gripping the sheet adjacent the groove; and scoring thecentral portion of the groove of the gripped sheet after the groove hasbeen formed so that the stress resulting from the stamping is absorbedin the inclined walls rather than being transmitted to the remainder ofthe sheet or to the tear strip.
 3. A method of forming a can end havinga manually removable tear strip thereon, including the following stepsin the order recited: clamping a relatively thin steel sheet on oppositesides of at least one elongate portion; forming an elongate bufferinggroove in said elongate portion of the clamped sheet having oppositesidewalls inclined at between about 60* and 90* with respect to themajor portion of the lid, and a central wall joining the sidewalls;clamping the sheet on opposite sides of the groove; and stamping a scorein the central wall of said groove of the clamped sheet to define theedges of a manually removable tear strip.
 4. The method of forming ascored tear strip on a steel can end in accordance with claim 1 whereinthe step of forming the groove includes the step of forming the grooveto a depth at least several times the thickness of the sheet.